FTS4060/S24 Cesium Frequency Std
Datum 4065B Time & Frequency Standard
Fast Test Method with SR620
4065B Frequency Offset
Symmetricom Chip Scale Atomic Clock
|Datum 4065B Cesium Time &
Frequency Standard top off showing three 8 Volt batteries.
On the right the toggle switch (advance/retard and the 7 thumbwheel
switches control the movable 1 PPS output in 100 ns steps.
The BNC just below the toggle is the programmable frequency TTL square
wave output (.1/1/5/10 MHz).
The yellow cap is on the 1 PPS master output.
The black cap is on the 1 PPS sync input BNC.
Two 7AH Gel Cell 12 Volt Batteries connected while working on the three
8V 5 AH batteries.
Just to the right of the line cord jack is a toggle switch which when
turned down shuts down all of the unit except for the ion pump.
A much better solution to storage than circuit mods.
The field of type-N connectors has 3 ea 10 MHz out, 3 ea 5 MHz out and
3 ea 1 MHz out all 1 Vrms, 50 Ohms.
The BNC above the DB-9 is the alarm status and the DB-9 is alarm info.
The DB-25 is a serial connector for data I/O.
This box does not have the optional telecom outputs.
The far top right BNC is the master pulse out.
Below it is the adjustable offset 1 PPS out.
|Getting ready to compare
them. You can see the family resemblance. Note both units
are locked and operational.
The 4060 is s/n 1227 and should be fairly close to on frequency.
Fast High Precision Set-up of SR 620 Counter
This idea is from the PRS10 Rubidium
Frequency standard manual appendix B.
- 10 MHz Reference to BNC-T on rear panel 10 MHz Input then to
front panel "A" start input
- 10 MHz DUT to front panel "B" stop input
- Front panel 1 kHz TTL REF OUT to front panel EXT Gate input.
- CONFIG - press SET to select cAL and press SELECT to choose
"cLoc SourcE", use arrow keys to set rEAr.
- in the Gate field: select POS, TERM = 50 Ohms and LEVEL= +1.0
- for sine wave 10 MHz inputs set the A and B input fields to: AC,
50 Ohms, Level full CCW, + Slope.
MODE to FREQ, SOURCE to B, GATE/ARM to 1 second and SAMPLE SIZE to 1
then hold START down for a few seconds, DISPLAY to MEAN.
This display should be within 0.1 Hz of 10 MHz
Fine Frequency Measurement
This will show 1E12 in one second.
MODE to TIME
SOURCE of Start to A
GATE/ARM to +TIME and EXT
SAMPLE SIZE to 1000 (1 & 103
Now each second there will be a display of 1,000 averaged
readings. This brings the 620 precision down to 1 ps.
Datum 4065B Cesium Time & Frequency Standard
The FTS4060/S24 is really a frequency standard and I've always wanted
an excellent time standard.
This unit came from an eBay ad showing a Major alarm and not
locked. But when powered up it locked in about 10 minutes and
after connecting the removed and taped battery wire and waiting an
additional 10 minutes the charge fault could be cleared.
Each of the three batteries is has four "X" 5 AH cells where each cell
Cyclon cylindrical sealed lead acid cell. The 2.5 AH "D"
used in the O-1814
Rubidium Time &
Frequency standard. The top of each battery is marked "bad" and a
date of 10-2-01. The voltage across the pack is now 31.2 VDC but
there probably is no current flowing if any one cell is bad, so some
testing will be needed to see what the real problem is.
Theory of Operation
This is a modern Cesium standard that uses control loops so that it's
frequency is correct, i.e. the C-field adjustment is automatic not
manual like the 4060.
Unlike the FTS 4060 where you manually set the C-Field this one
monitors and adjusts based on the following items as reported in the
Status 5 menu:
-10 S.B. <= 160 mv
Rabi-Ramsey Error 0 S.B.
<= 40 mv
-15 S.B. <= 160 mv
Rabi-Zeeman Error -4 S.B. <=
Ramsey Confidence +3 S.B. <=
The AC mains power a 31 VDC supply that's diode ORed with the internal
battery and the external DC supply. The internal supply is a 24
Volt lead acid battery, 12 cells of Cyclon "X" size cylindrical sealed
pure lead acid. There are a couple of major problems with this:
- The temperature inside the case is always warm to almost
hot. That degrades the life of the lead acid battery by an order
- If there's any venting, like happened with the Gibbs double oven
crystal oscillator, the fumes and heat make a good combination to etch
the traces right off printed circuit boards.
So, rather than replacing the internal lead acid battery, it will be
connected as an external battery. Since a diode OR gate is used
to combine the three power supplies a new wire needs to be run to one
of the unused pins on the external battery connector to bring out the
internal battery terminals to allow float charging.
The Red-Black Siamese cable has male 1/4" Faston connectors that match
those on the batteries and so plug into the internal battery wiring
connectors. The white label says:
Remote Internal Battery D: -24, E: +24
The Plug in the lower right of the photo connects D to black and E to
Red. The other end of the cable has female 1/4" Faston connectors
to plug into the battery. This solves the two major objections to
an internal battery, i.e:
- If battery vents acid fumes they will not
destroy the expensive circuitry
- The battery will last 3 to 10 times longer when
running at room temperature
Pins D and E on J100 External DC Input were spares and so a true
external battery can be added just be wiring it to pins A (positive)
and C (return). Note the external battery must have it's
own charging circuit and should be at some voltage level chosen by what
priority it should be used.
4065B Frequency Offset
On the FTS4065 the C-Field adjustment is made by the internal
microprocessor and there is a seperate Frequency Offset adjustment.
After plotting for the time interval between the 4065B and GPS from 5
May to 7 May (4065plot9.pdf
and finding a straight line with a slope of 472E-15 the Frequency
Offset was changed from +000000 to +000472 (a 50-50 gamble that the
sign should be +).
new plot was started 7 May after the change and for the first couple of
days seemed to have worked. By starting a new plot I mean that
constants were subtracted from the time interval so it starts at 0.0
and the starting second count starts at 0.0. This way is the plot
is a straight line it can be forced to go through (0,0).
By May 10 at 9:50 am it looked like the frequency offset had
worked. The data (plot10a.pdf
in a box about +/- 10 ns high after 2 3/4 days (3E-13) but more time
needed for good data.
Then the points started a climb. By 14 May (4 days later) the
data between May 10 and 14 looks again like a nice straight line
(plot10.pdf)with a slope of about 472E-15. BUT the frequency
offset is still set at +000472. (4065BvsGPSp10b.pdf
The 4E-13 number floating on the plot is the slope after one day.
Just put it there so I could remember what it was. Excel
recomputes the slope as each new data point is added.
The 4065 box was rotated 90 degrees and it did make a good sized change.
Before this plot was started the frequency offset was stable at 472
(parts in E-15) and the 4065 Frequency Offset was set to +472.
For the first couple of days it looked like that change was working and
the frequency offset was near zero.
But then the frequency offset returned to +472 (this with the Frequency
Offset dialed to 472) and that continued for over four days when I
turned the 4065 box 90 degrees clockwise (just prior to the day 7 grid
line). That made a big change and now (May 17 2008) the slope is
more like 167 (parts in E-15).
It may be that the Earth's magnetic field is having an influence or
maybe just the mechanical shock has the influence.
Any thoughts what's going on? Contact
Model Numbers & Options
Setting C Field
Manual Control Voltage & Loop Gain Setting
Government Liquidation Warning
A common misconception (and one that I
had until working with a Cesium standard) is that the timing is
perfect. This is not the case. A Cesium standard wanders
around the nominal frequency, but may not drift like a crystal
oscillator. A couple of terms will help when
working with this concept.
Offset - is a measure of how
close to the desired frequency an oscillator is running. For
example an oscillator that's supposed to be at exactly 10 MHz is off by
0.0001 Hz has an offset of 1E-11. The offset is only valid at the
instant when it was measured. It's measure a of how well someone
set the frequency not so much about oscillator quality. Since
this is something that's under the user's control a lot of time and
effort go into minimizing the offset. It's common practice when
setting the frequency of a lab grade crystal oscillator to set it right
at the edge of the system spec, but on the side where aging will move
the frequency so it at first gets better, then it's perfect, then it
moves to the other side of the spec. In order to do this the
aging rate (i.e. stability) needs to be known.
Note that a Cesium standard may not be set to have a zero offset, but
rather most end up with an offset on the order of parts in E13 or
E14. The offset is known and can be backed out of measurements on
other time standards. But if the Cesium standard will be driving
a clock or say a transmitter, the setting the offset to the lowest
possible value is important. The key thing is that there is no
aging, i.e. a time interval plot vs. GPS will be a straight line
whereas a crystal or Rubidium oscillator will have a parabolic plot.
Stability - Stability is the
money spec. a measure of how
well the frequency stays the same. A perfect oscillator would not
change frequency with time, power input, temperature, etc., but you
can't get that one. The measure of how the frequency changes with
running time is called aging. The specification on the HP
(Agilent) 5071A Cesium standard ($50k) is less than 1E-14 per
day. . That's to say that if it was set with a zero offset
today, by tomorrow noon it might by off frequency by 1E-14.
The plot at the bottom of web page http://www.niceties.com/utcdwh.html
(650 days of data) shows what might be a random walk of around plus and
minus 100 ns for an HP 5071A.
My s/n 1227 is running at abut -1.4E-14 per day. It would be a
tad out of spec for the HP 5071A. Cesium sources are NOT supposed
to have aging ike this.
Cesium standards are a step better than
Rubidium standards and are the basis of the definition of a
second. But that does not mean they are "perfect".
These are the S24 option that has a 1 MHz front panel
output, NSN 6625-01-245-3092. The official definition of a
second of time is exactly 9,192,631,770 oscillations of a Cesium atom
between the F3 and F4 states.
The HP 5060
was probably the first commercial Cesium standard. It was all
analog, no microcontrollers then. HP took over the Varian line of
Cesium standards. Then when HP and Agilent split, Agilent kept
the Time and Frequency instruments and HP then became a computer and
The FTS4060 I would call a second
generation Cesium standard because it
has a micro processor that replaces a lot of analog circuitry and is
much easier to use. There is a manual C field adjustment that
needs to be set where the coarse thumb wheel is 1E-12 per tick and the
fine wheel is maybe 1E-14 per tick.
These were purchased from
Government Liquidation with a condition code of "A1" which should mean
that they are new. Here are some dates:
date on Lid
|1 Mar 02
|23 Apr 01
|1 Mar 02
Possible meaning: The first control
voltage measurement was done at the factory as part of the final
inspection and so is close to the ship date. These dates and the
serial numbers are in the same order. The front panel date may be
when the units were tested prior to being put up for auction.
These dates seem to be over 2 years prior to the auction date which may
be due to how fast the government surpluses them. Note that it's
about 14 years from the final test date to the surplus date. So
maybe there is some number of storage years after which these units are
surplused, say 15 years.
s/n 1013 was shipped outside it's carton and failed to lock when
received. Opening the bottom of s/n 1013 shows the Cesium Beam
tube, Brick power
supply, and fancy 10 MHz crystal oscillator plus other
components. Behind the Cs tube is paper work indicating it was
replaced in 1996. There must be some reason that s/n 1013 is not
working, need a manual to find it. In the left photo at the top
of this page notice that the green "LOCK" light is on for the top two
standards (1033 & 1227) and off on the bottom (1013) one.
Model Numbers & Options
The normal FTS4060 comes in with either
a 10 MHz optimized output (/201) or a 5 MHz optimized output (/101).
The /S24 option was a special unit made for the U.S. military and has
only a 1 Mhz output on the front and rear panels and does not have
other frequencies as outputs and does not have the 1 PPS output. It
does not have the internal or external DC supply options. It's a
stripped down model.
All of my units (s/n 1013, 1033, 1227 have the SMA-f connector on the
A5 Distribution Amplifier Assembly, but not all /S24 units have this
connector. It's the 10 MHz output at about 4.4 V Pk-Pk.
My s/n 1013 has a rear panel with a number of plugs like it was the
same rear panel used for a full featured 4060, but s/n 1227 has a solid
rear panel with no plugs, so in order to install the 10 MHz port I
moved the alarm connector to the inside of the box and replaced it with
the 10 MHz output.
Note that some FTS 4060 use a 5 MHz OCXO and others use a 10 MHz OCXO.
061 - 1 MHz and 100 kHz RF outputs
116 - Time-of-Day Display and 1 PPS Advance/Delay
117 - 1 PPS Advance/Delay
010 - Internal Battery and Charger
015 - External Standby Battery Supply
013 - Chassis Rack Slides
Just plug in the line cord, set the Mod
switch to ON and the LOOP switch to CLOSED. After something like
10 minutes to 30 minutes the green LOCK light will turn on and the
ALIGN pushbutton-lamp will turn off.
You can manually press the Red Operation Alarm Light/Switch to turn it
Pressing the AC Power Reset switch will turn off the red Alarm light.
Pressing the Align Light/Switch may turn it off or initiate a new align
The Voltages shown on the meter have been scaled to fit the meter's 0
to 5 volt range and are not the actual voltages in the circuit.
Near the brick power supply on the top side there's a Molex type
connector with Red, Black and Orange wires. The connector is the
same 4 terminal connector as used for hard drives in PC
computers. To get a mating connector buy a "Y" PC power supply
cable. You can tease out the male pins using a jeweler's
screwdriver if you don't have the extraction tool ( a hollow tube that
fits over the male pin). The reassemble with the black wire going
to the black ground wire in the FTS4060, Red to the +30 wire and yellow
going to the orange +5 volt wire. This makes for an easy way to
connect both an external DC backup supply, like the Austron 1290A and
also to supply 5 volts for a 1 PPS divider.
Setting C Field
23 May 2006
Until about a week ago I was using
the GPS 1 PPS as the start pulse and the 1 Mhz output from the FTS4060
as the stop pulse into a Stanford Research SR620 Time Interval Counter
and doing 500 second averages. There are some problems with this:
- The 1 MHz signal only allows a TI range of 1 micro second
before rollover occurs.
- When you get near the rollover the average value includes
data from both sides of rollover and is very wrong
- MOST IMPORTANT the noise is much higher than it needs to be!
By changing the setup so that the FTS4060 10 MHz output feeds the SR620
rear panel Reference Input (and setting the counter to use the external
reference frequency) and then using the front panel 1 kHz Reference
output as the stop signal two things happen. The rollover time is
now 1 milli second (10,000 times longer) and the noise is reduced
(probably SQRT(10000) = 100) by a huge amount.
With a 1 MHz stop if the TI is between 0 and 200 or between 800 and
1000 there is a chance of rollover points being in the average and
between 0 and 100 or between 900 and 1000 it's almost certain that
there will be rollover points in the average. Because of this I'm
currently slewing s/n 1003 which was at 980 ns and may have an optimum
C-field setting of 908 by setting the C-field at 000 where the slew
rate may be in the +20 to +40 ps/sec area so it sill take many hours to
get the TI to about 500 ns.
Note that the 1 kHz out and the
cable between Ref Out and B in, have an associated time delay so the TI
numbers will not match those with a direct connection.
17 May 2006 s/n 1227
By plotting the offset vs. C-field switch setting it's clear that the
slope is -1E-13 per tick. This is also a great way to see which
data points are not valid. For example the old data point for
C-field setting 492 was +9.8E-13 which is maybe 10 times higher than
where it may end up. As of 22 May 2006 it's -6.24E-14 with R2 of
0.84. When R2 gets up to one or two nines,
then we'll see.
Note that a Cs frequency source is just
like any other high stability source and needs to have it's frequency
set. The big advantage of Cs is that once set it will not drift
like Rb or Quartz. Note this is because of the defination of
time, and maybe is not reality.
15 Feb 2005 - The time interval plot was drifting up so an adjustment
was made to the C field. It turns out that the adjustment was too
large. 24 hours after the adjustment for abut 6 hours the time
interval stayed constant within about 10 nano seconds. This
indicates that even 24 hours after a C field change the frequency has
not stabilized. It really does take two to three days for
the unit to stablize after a C-field change.
Slew using C Field
9 March 2006 - When using a time interval counter where the start
signal is the 1 PPS output from a GPS timing receiver and the stop
signal is from the 1 MHz output of the FRS4060 the counter has a range
of 0 to 1,000 nanoseconds. If the time interval rolls over you
get a saw tooth type plot. In order to slew the time interval
away from 0 or 1,000 you can set the C field as far as possible from
the correct setting. For example on s/n1013 the correct setting
will be near 855, so setting to 000 causes the frequency to slew at
about 1,400 ns per day which is an offset of 1.6E-11 but you can
see to get a 500 ns change will take about 8.5 hours. Not as fast
as you would like. There may be other ways to slew, but so far
Note that when the C field is misadjusted as much as possible (1.6E-11)
the offset is 10 to 100 times better than the best ovenized lab grade
crystal oscillators daily aging rate(1E-9 to 1E-10).
Thumb Wheel Switch Sensivity
11 Dec 2005 - s/n 1013 after complete dissassembly and reassembly seems
to be working, not like in Jan 2005.
With C field thumb wheel switches set for 500 the plot of (start = GPS
1 PPS, stop= FTS4060 1 MHz zero crossing) has a positive slope of about
5.7864 ps/sec and the plot with C field at 900 has a slope of -1.7764
ps/sec. So the thumbwheel switches may have a scale factor of:
Scale Factor = (7.5628 - (-1.7764)) / (900 - 500) = 0.023348 ps/sec or
about 2E-14 per click.
See framed coment above the scale factor for s/n 1227 is -1E-13 per
When making a Time Interval measurement
there are different signals that can be used. The common ones are
a 1 PPS, 1 MHz or 10 MHz. The big advantage of the 1 PPS signal
is that it takes a long time for a 1 second rollover. If the TI
counter is triggered with a 1 PPS pulse (like from the PSR10 Rb source)
and the 1 MHz output from the /S24 Cs source is used as the stop signal
to the SR620 then the data will have a range of 0 to 1 micro second.
(i.e. the period of the 1 MHz signal). If the Cs source can be
off by as much as 1000 counts where each count is 1E-13 then it might
be off by as much as 1E-10. When the 1 MHz output is used as the
stop signal then rollover might occur every 1000 seconds. This
means that the TI needs to be measured a number of times inside each
1000 second period. You can not just measure at times seperated
by 24 hours when the source stability might be as bad as 1E-10.
If a 1 PPS stop signal was available from the Cs source then there
be no rollover problem since a source with 1E-10 stability will only
drift 8.6 micro seconds in 24 hours.
I have a WWV clock and when the 1 PPS from the PRS10 is used to trigger
the A counter input the counter trigger LED is flashing at exactly (as
seen by eye) that same time as the WWV clock changes seconds.
This makes it easy to tell which reading is axactly on the minute for
manual recoring into an Excell spreadsheet.
If the 1 PPS output from a Motorola
M12+T Timing receiver had the sawtooth corrected so that it was not
modulating the 1 PPS position then the time needed to set a Cs standard
would be reduced by a factor of 10 or more. For example if
instead of an uncertatiny of +/- 50 ns on each pulse the uncertanity
was +/- 1 ns then instead of needing 50,000 seconds (13.8 hours) to see
1E-12 you would only need 1,000 seconds (16.6 minutes)
WRONG #1- Since the saw tooth
error is symetrical it gets removed when averaging is done. On a
500 second average using the GPS 1 PPS as the start and the SR620 1 kHz
Reference Out as the stop the standard deviation on the group of 500 is
right at 9 nano seconds, but the mean value is independent of the
WRONG #2 - 50 ns is the saw
tooth size for the older 8 channel Motorola timing GPS receivers, but
the M12+T only has a 9 ns saw tooth.
Direction of Change
If the time interval has a positive
slope then the period of the FTS4060 is increasing and so to reduce the
period the frequency should be increased and so the thumb wheel
switches should be moved to a higher number. This is for the case where
start is GPS and stop is the FTS4060.
One way to adjust the C field 3 digit thumb wheel pot is to use
GPS. Although there is some jitter on the GPS 1 PPS signal that
amounts to maybe plus and minus 50 ns (Motorola 8 chan), the accuracy
over a 24 hour
period is on the order of 1E-12. The Motorola M12+T has about 9
ns and so is much better. The GPS receiver should be used
directly. Also there a lot of jitter on the 1 MHz FTS4060 output,
much better to divide it down to 1 kHz or 1 PPS.
It seems that the scale factor for the /S24 using is 1E-13 per count
NOT the 2E-14 in the normal FTS4060 manual.
9 Jan 2005 - Plot
10 Jan 2005 - Plot of nano
seconds of Time
vs seconds of running time
for s/n 1013 - 5.9E-12?
12 Jan 2005 - Plot
Between 124,920 and 169,680 (12.4 hours) the 1 PPS input to the PRS10
was removed and when reconnected caused a negative swing that lasted
until 248,400 seconds. But it appears that a C-Field setting of
913 is pretty close to correct. The drift is in the e-13 ot E-14
18 Jan 2005 - Plot of s/n1013 vs. s/n
, 1227 vs GPS & 1013 vs GPS, now using s/n 1227 as 10 MHz
ref for SR 620 counter.
s/n 1227 has it's C Field set at 600 as received from Govt Liq. and it
appears to be moving at -3.6E-12. s/n 1013 seems to be moving at 5E-10
more like an OCXO than a Cesium, but the Lock LED is on and the beam
current peaks as it should. What wrong?
1 Feb 2005 - s/n 1227 - I tried to use the time interval between GPS
and the 1 Mhz output to set the C Field by getting the offset and then
dialing in the correction (it looked like the three thumb wheels were
1E-12, 1E-13 and 1E-14), but the resulting slope after a few days of
observation seemed to overshoot. A better way would be to use a
binary search where at each attempt you would half the error. I
think I have the setting to within a single count on the finest wheel,
but it'll take some days to see.
10 Feb 2005 - s.n 1227 - Still have C
field at 544
. The 10 day plot shows GPS wandering within a
150 ns range so the poorest stability might be 1.7E-13, but an average
would be more like parts in E-14.
10 Feb 2005 - Enabled Ionospheric correction in GPS receiver and the
delta time jumped up to the 500 ns range, so this may account for the
100 or or ns variation the last 10 days. More time will tell.
11 Feb 2005 - changed GPS to track 4 highest satellites and changed
elevation mask to 30 degrees.
It's very important that the GPS receiver is properly setup to get the
best timing results.
28 Feb 2005 - The C field has been at
for about 9 days and on average there does not appear to be any
drift, but it's difficult to tell.
2 March 2005 - To improve the stability of the GPS 1 PPS I increased
the elevation mask again, this time from 30 degrees to 50
degrees. It has made a big improvement. The standard
deviation after 1,000 seconds worth of 1 PPS averaging is now in the 30
ns area where before it was in the 200 ns area. During 3 days of
observation there never was a time when there were no satellites above
50 degrees. Since I'm running the GPS receiver in the timing mode
(known antenna position) only one satellite is needed for a timing
8 March 2005 - C filed at 565
After the problem with the 4060 going crazy after a beam current
centering. Needed to cycle power to get good operation.
13 March 2005 - Yesterday the counter got unplugged, but neigher the
FTS4060 nor the Austron 2100T were unplugged. Both of these
instruments have warning LEDs that would indicate a loss of mains
power, but the FTS-4060 output frequency became more unstable after
this event. This morning I unplugged the FTS4060 for 10 seconds
and restarted it. After that the standard deviation on the time
interval improved from over 300 ns to more like 30 ns. Maybe
there are some power supply caps that need replacing or more caps need
to be added?
Also the amount of averaging on the GPS 1 PPS needs to be
increased. At 1,000 averages the best stability that can be seen
in one day is about
(3 * 35 ns * 2) / (SQRT(1,000) * 86400) = 7.6E-14, but by going
to 5,000 seconds the system improves to 3.4E-14. So starting a
15 April 2005 - Switched to an SynPaQ/III with Motorola M12+T GPS
receiver. This unit has 3 to 4 times less variation than the old
8 channel UT+ GPS receiver. But there appears to be a parabolic
change in the plot
over the past 5
weeks that I don't understand. The C filed has been at 568 since
20 March 2005.
28 April 2005 - the plot for s/n 1227 vs both GPS and Loran-C still
appears to be parabolic
some type of aging which is NOT supposed to occur whith a Cesium
source. Aging is about -3E-14 per day.
29 April 2005 - the aging rate
seems to be slowing down. It's now -2.2E-14/day.
1 Feb 2006 - s/n 1013 seems to be working after having all the modules
taken apart (working on technical manual) and then put back toghther
again on 9 Dec 2005. Changing the C-field causes a change that
takes about a week to settle down (now C=850) and for the last few days
the 1 PPS has stayed within about 1 ns of the Motorola M12+T pulse
(maybe 1ns/3 days = 4E-14).
6 Feb 2006 - s/n
is showing drift like s/n1227. The equation for s/n 1013
y = 2.7943x2 - 302.64x + 8969.4
quality of fit is
R2 = 0.9088. The x-axis is in days and the y-axis is in ns.
The first deritive of the equation has a first term of 2 * 2.7943 * x
ns/day or +5.3E-14 drift rate.
I don't know if this is a measurement problem or a problem with the
9 March 2006 - The apparent parabolic aging was a measurement problem
related to setting the time interval counter trigger level improperly
(50 Ohm source and load TTL should be at 1.25 Volts, NOT 2.4 volts).
Now s/n 1013 is looking very good. Another problem may have been
that the Ultra Stable Oscillator coarse frequency was not set
properly. It now has been centered and now looks like +4E-13
offset which I'm trying to adjust to be much better.
28 April 2006 -
GPS has some noise. For example the Motorola M12T+ has a standard
deviation of about 9 ns when 500 Time INteval readings are averaged
(reference is some good oscillator). So you might expect that the
noise will peak +3 sigma and -3 sigma from the mean value. This
means that the offset you can see is about 54ns/(measurement time in
|1 to 4 min
|15 min to 1
|1 to 4
|12 to 48hr
|1 - 4 days
|week to month
When plotting Time Intervals in Excel you can fit a trendline and also
get an R squared quality of fit number. R^2 should be some number
of nines for a good fit. If it's not then there's something wrong.
17 May 2006 - there are times that last for about a couple of hours
whee the SR620 is displaying a standard deviation for a 500 second
average as high as a few hundred nano seconds. I still don't know
what causes this. Some possible things that might cause it are:
- multipath may cause a problem if there was only one or two sats
visable, but I would think with 3 or more visable a poor satellite
would not cause a problem?
- no satellites at all would allow the GPS receivers 1 PPS to be
coming from it's raw crystal
- some problem with the SR620 - I have disconnected the PRS10 as
the external ref since it's not needed and between the PRS10, it's
power supply, GPS receiver there's just that much more to go
wrong. But this has not seemed t make any difference.
Instead of connecting the cesium 1 MHz signal to the B input, connect
the 10 MHz signal to the counter's rear panel 10 Mhz input. Use
SEL, SET & SCALE^V to enable rear clock input. Then connect
the front panel 1 kHz Reference TTL output to the B (stop)
input. Now the rollover will be every 1 mS, or a thousand times
The problem was that the data was
getting near the 1,000 uS rollover point caused by using a 1 Mhz signal
for the counter B (stop) input.
If you're using Julian Day numbers (maybe 6 digits) and have less that
20% of the JDN worth of data, the Excel trendline will be in
error. Much better to subtract a very large constant from the JDN
so that the x-axis starts from zero. This way the trendline is
The number of data points should be the same on either side of a
straight trend line. In my case ALL the data points were on one
side of the line.
The LORAN-C system will continue and
will be improved (2005) and offers a high quality time transfer
The Austron 2100F
will work for this application.
The HP 5060A manual says the Zeeman
frequency should be 42.82 kHz and about 1 volt RMS. And that an
error in the Zeeman signal of 1% translates into a Cs frequency error
of 3.6E-12, so it needs to be set to within about 1 Hz. The
amplitude of the Zeeman signal and the C-Field
can be adjusted, with the modulation off and the loop open to set the
C-Field, or the C-Field can be measured by adjusting the frequency and
amplitude of the Zeeman input to get maximum beam current.
Mr. Pieter Zeeman won the Nobel
along with Mr. Lorentz for explaining a
splitting in the spectral lines of light caused by magnetic
fields. This explanation was based on the new things called
"electrons", but did not take into account quantum effects like up and
down spins. His experiments and the theory by Lorentz shed a lot
of light on what an "electron" was.
So far I don't have an audio generator that has the required frequency
settability AND enough drive power to do this test.
Corby D Dawson and Tom Van Baak have described how the audio frequency
for the Zeeman effect depends on the physics package and I'm rephrasing
it here. The definition of the second is based on a Cesium
standard running in a zero magnetic field at sea level with a frequency
9192.631770 MHz. Real Cesium tubes run with a very small magnetic
field and so their frequency is slightly off that for a standard
second, but the manufacturer knows how far off and allows for it so
that the final 10 MHz or 1 PPS is exactly correct.
milli G 1
- The C
field coils in both HP and FTS Cesium tubes have the same milli gauss
per milli amp constant and so the C field is determined by how the main
frame is setup.
synthesizer that generates the frequency that's fed to the multiplier
is also in the main frame and has a frequency that matches the strength
of the C field.
Note that as long as the C field and synthysizer are matched to each
other the system should work properly.
was a scheduled power outage
whicl PG&E replaced a power pole. Since I still have not got
the Austron 1290 Back Up power supply operational, I juse connected a
couple of 12 Volt 7 AH gel cell batteries in series with a SB360
schottky diode. Using the male plug from a PC hard drive power
supply "Y" cable with the pins reisntalled so that black goes to black
(ground) and red goes to +30 and Yellow goes to orange (+5) and with
the diode cathode to the 4060 + 30 volt line the batteries held up the
4060 for the 3 hours the mains power was down. Now I have removed
the batteries and a charging them manually with a bench supply.
The 12V 7 AH lead acid batteries are 3.75" from the bottom to the top
of the metal terminals. The distance from the bottom of the
battery shelf to the bottom of the lid is about 3.75", so it would be a
bad idea to try and close the lid with the batteries inside. And
there's an even more compelling reason to NOT put lead acid batteries
in the same box as electronics. And that's because acid fumes
from the lead acid battery will literally eat the traces off the
printed circuit boards. So it's best if the batteries are out of
It took about 2.7 AH to charge one of the 12 V 7 AH batteries and the
power outage was about 2.7 hours, so the FTS4060 is pulling about 1 Amp.
But the 7 AH rating is for a 20 hour discharge (350 ma) so the battery
will not last 7 hours at 1 amp. I think the terminal voltage at
the end of the power outage was about 23.49 volts or 11.75 volts per
battery which is discharged. Maybe 2.7 AH is the capacity at 1
When running from the batteries the Green Lock LED is on and the red AC
Power Alarm LED is on as well as the red Battery LED. But monitor
position 6 still shows 0 because there is no charging current.
After AC power is restored the Power On Green and the red Powere Alarm
are both on (press the reset button to clear the red alarm LED).
The green lock LED is still on. No battery LEDs are on.
(remember the /S24 has no battery option.)
Dead New Batteries
At first one of the new batteries not only would not put out any
voltage, but actually had reverse voltage across it and the 4060 was
still running. This means that the switching supply will keep the
4060 going on less than 12 volts (although it may or may not start a
cold 4060 on that low a voltage). The "bad" battery looked just
like the good batteries when connected to the charging power
up a simple 12 Volt battery checker
that's just a number 1156 car tail light bulb soldered to a clip lead
that was cut in half. This pulls a couple of amps to light
brightly and with only 1 amp will take some seconds to light
dimly. This works much better than the Radio Shack 22-080 battery
tester that shows a dead battery as good.
Note that the very common 12 V 7 AH batteries come with both 1/4"
(0.250") and 3/16" (0.187) quick connect type terminals. On the
batteries I got some are 1/4" and some are 3/16". So you need to
check each battery, even though at a quick glance they look the same.
Under the top cover the brick power supply is on the right.
Beside it is a tray that could hold rechargeable batteries.
There's a 4 position Molex connector with 3 sockets installed on wires
that are Red, Black and Orange marked "26" that's probably the battery
pack connector. There is a PCB behind the left metered panel and
another PCB behind the
setup controls located behind the door on the right.
Chicago Miniature CMD series LED's.
Yellow CMD 53124A
The upper left box is marked Model 5030M/201/S25, s/n 199, U.S. Patent
Autolock for resonators for frequency standards Feb 12, 1985 Class 331/3
A system is disclosed for examining the response in atomic
and molecular resonators to identify and select the maximum resonant
peak and the voltage used to cause said peak to be produced. The system
is fabricated of modular elements electrically connected to a circuit
board to facilitate its construction and transportation with the
resonator. A microprocessor is utilized to perform the analysis and to
generate information to select the maximum resonant peak, and the
system includes means to compare the value of successively generated
resonator outputs and to select the output with the maximum peak.
331 is Oscillators and /3 is Molecular resonance stabilization
The idea of this invention is to use a microcontroller (RCA or Hughes
1802 CMOS) to sweep the control voltage to the 10 MHz OCXO across it's
range and watch the CBT output peaks and valleys. By looking for
a peak with aproximate equal valued adajacent valleys on both sides the
maximum peak can be selected and that peak used to lock the servo
system tying to CBT to the 10 MHz reference. The three DAC1006
to Analog converter chips that are part of the A/D system reading the
output voltage is potted in a clear compound probably to reduce elakage
currents. J2 is the OCXO control voltage output.
Atomic beam tube
June 29, 1976 250/251; 331/3; 331/94.1 by FTS (3967115.pdf
Other FTS Patents
Digital frequency generation in atomic frequency standards
using digital phase shifting February 24, 1998 331/3
Methods and apparatus for digital frequency generation in
atomic frequency standards February 3, 1998 331/3; 331/94.1
Heater controller for atomic frequency standards August 12,
Resonator package for atomic frequency standard May 6, 1997
System for producing spectrally pure optical pumping light
August 29, 1989 359/345
Adjustable crystal oscillator with acceleration
compensation May 13, 1986 331/156
Crystal oscillator assembly April 29, 1986 331/69
4899117 High accuracy frequency standard and clock system, Vig; John R,
Feb 6, 1990, 331/3 ; 331/176; 331/44; 331/47; 368/202; 368/56
"Moreover, in rubidium frequency
standards, the available C-field
adjustment range limits the useful life of the unit. For example, in
one of the most popular rubidium frequency standards currently on the
market, the manufacturer provides a C-field adjustment range equivalent
to +1.5.times.10.sup.-9. The aging rate of the standard is specified as
2.times.10.sup.-10 per year. Consequently, at the specified aging rate,
the limited C-field adjustment range
limits the useful life of this rubidium frequency standard to
1.5.times.10.sup.-9 /2.times.10.sup.-10 =7.5 years."
5146184 Atomic clock system with improved servo syste
331/3 ; 331/79
Inside the 4060/S24
J3 is the signal coming from the I/F
PCB of the CBT.
J4 is the
450 Hz output to the A7 X18 multiplier.
There is a 40 conductor ribbon cable connection, 2 coax cables and a
cable with 2
wires (Red and Black) going to A7 and TP2.
2:50 power on TP2 = 4.97 VDC and the front panel meter on 4 (control
voltage) indicates about 5 volts. (2:50 pm)
2:56 Operation Monitor light turned off.
3:00 switching LOOP to Open and back to closed starts meter into
sawtooth from 0 to 5 Volts. It takes about 21 seconds to sweep the
monitor voltage from 0 to 5 Volts.
But TP2 is sitting at 4.98 VDC so must be a 5 Volt test point or it's
some logic indicator that may be pointing to a problem.
21 July 2005 - A3-TP2 a test point to monitor the 450 Hz signal that
The Cesium Beam Tube is on the right, marked: Cesium Beam Tube, Model
FTS-7103, p/n 08923-501, NSN 5960-01-214-7475.
To the left of the CBT at the rear is the 10 MHz oscillaotr, marked:
Model 1000B. In front of the 10 MHz osc. is The A5 Distrubution
Amp metal box with an
SMA-f connector just behind the front panel marked J3, RF1 which may be
a 10 MHz signal that could be connected to the front or rear
center divider is the A3 Alarm PCB
2 each DB-25 connectors and no RF coax connections. Marked:
D.1652 s/n 865009 (probably 1986 +...) It is not
fully populated, missing a few ICs and a number of discrete
parts that probably are part of the battery charging or monitoring
circuit. The 30 VDC brick power supply is up aginst the left wall.
I have named the DB-25m connector nearer the powr supply A3J1 and the
DB-25m near the center divider A3J2 since there's no markings on either.
A3J1 pins 23, 22, 24, 25, 2 and 6 are connected to the Monitor thumb
wheel switch positions 1 thorough 6 respectively and the switch common
goes through the front panel meter to ground.
The Battery Charge, AC Power Alrarm, Battery On andAC Power On LEDs are
connected to A3J1 pins 4, 5, 6 and 9 respectively.
Five of the wires on A3J2 are connected to the 5030 Assembly J1
A3J1 pins 1, 13 and 18 and connected to A3J2 pins 1,2,5,6,8,13 which is
The Physics package might be defined as
the combination of the Cesium beam tube, the Times 51 Multiplier and
the Interface PCB since the latter two items are bolted to the side of
the Cesium Beam Tube.
The Physics Package is in turn a part of the 5030 Assembly. In
addition to the Physics Package the 5030 assembly has Most of the parts
except the PS1 30 Volt power supply and the A3 Alarm 5 x 6" PCB, and
the front and
rear panels. The 5030 Assembly is 16 x 7.75 x 5 inches.
the four 5/32" hex cap bolts, being
careful to not let the 5030 assembly crash and move it so that you can
easily get to the SMA connectors and the #2 Philips screws on the "D"
Check to see that the 3 Coax cables are marked 4 (Zeeman audio in), 5
(Rear 1 MHz out) and 7(Front 1 MHz out) that mate to
J4, J5 and J7, then disconnect these SMA cables.
Remove the two "D" connectors using a #2 Philips screwdriver and lift
the 5030 Assembly free of the chassis.
Note It is an easy job to replace the
5030 Assembly and that may allow using the complete 5030 Assembly from
/S24 unit to bring a defunct FTS4060 back on line. This can be
done in a few minutes. But I don't know where the additional
modules are located on a full featured 4060. If they are on the
right side ( the 5030 is on the left side) then it would be very
easy. If they are in the way of removing the 5030 Assembly then
it would take longer.
10 MHz OCXO.
A1A5 Dist AMP
At the upper right is the A5
Distribution Amplifier. This amy be an A5/S24 with the front 10
Mhz output missing.
A1A5 & A1A7 Sub Assembly
cable ends that will be disconnected, then
by removing 2 (+) screws and loosening 2 (-) captive screws and
disconnecting some connectors (no soldering needed) the combined A5
& A7 assembly can easily be removed.
A1A5 Distrubution Amp
units have an A5 amplifier that has a open SMA-f connector facing
forward and that connector has a 10 MHz signal that's about 4.4 Volts
Pk-Pk. But other /S24 units have the connector and some internal
parts removed and so don't have the 10 MHz easy to connect.
The cable from the A5 10 Mhz output to the rear panel is about 40"
long, SMA(m) on the A5 end and a bulkhead BNC(f) for the rear panel
A1A2 Mother Board
be seen once the A5+A7 sub assembly is
removed. All the components in the 5030 assembly interface to the
mother board. This greatly minimizes the wiring clutter.
There may be a dozen components on the mother board.
Max dimensions are about 12" x 5" although it's "L" shaped.
the A1A9 input filter at attached to the
The right hand narrow part is just to get the 40 conductor ribbon cable
lined up with the A1A3 uP board.
A1A6 Ultra-stable Oscillator
). This is a brick about 3x3x7inches with all the
connections on one of the 3x3" ends. Part number is
05818-119. There's a DB-9 connector
with the following pinout:
Voltage in (-10 to +10)
|+12 V ref
(coarse tune hot)
|+24 VDC Oven
+24 VDC pwr
The oven insulation is my means of a dewar. The initial aging
rate might be <1E-10 per day when new, but can get below 1E-12 after
running for some time. The phase noise is lower than -134 dB at
10 Hz, -144 dB at 100 Hz and -157 dB at 1 kHz.
The 10 Mhz output is from a right angle SMB connector pointing
down. (All the small coax is terminated with 50 Ohm SMB
connectors in the FTS4060).
On top of the 1000B (p/n 05818-119) there's a coarse frequency
To remove the USO three 1/4" nuts need to be removed that are below the
A3 uP board and the connectors disconnected.
on a hand picked 100B:
A1A7 x18 Mult & Mixer
the Times 18
Frequency Multiplier (10 MHz in, 180 MHz out) and mixer.
As seen in the photo the connectors are: 10 MHz in, connector
with Black, Gnd, and Red wires going to J4 on
the A3 Microprocessor board. Cable with Black, Red, Green
(ground) & blue wires soldered to feedthroughs going to connector
J4 on Cesium Beam Tube motherboard.. 12.6 MHz input & 180 MHz
A1A8 Cs Power Supply
A8 Power Supply for the Cesium Beam Tube that
includes the two HIGH VOLTAGE outputs. The bottom of this PCB is
the top left front when the top cover is removed. You might not
want to have your hands anywhere near this board when power is applied.
A1A9 DC Input Filter
slot and should be able to slide out, it's trapped by
the female thread fitting used to attach the 5030 sub assembly to the
chassis. It has a dual electrolytic cap, a single electrolytic
cap, a diode and an inductor.
A2 RF Assebmly
3 x 7" A2/S24 RF Assembly (56219-05280-011
Assy 05281) that takes in 10 MHz and outputs 1 MHz. On a full
featured 4060 this board would also output 100 kHz and 10 MHz.
may that the 74LS90 divide by 10 circuit could be bypassed to
10 MHz outputs instead of the two 1 MHz outputs that are on the /S24
A1A3 Micro Processor Board
input (J2) that takes in the error signal from the
Cs interface board. It also has a coax EFT output (J3) to drive
the Ultra-stable 10 MHz oscillator (A6). The 450 Hz signal is
generated on this board and feeds A7. 40 pin connector J1 has a
number of analog signal inputs and outputs as will as digital inputs
With J1 pointing up in the photo at left the two TO-5 cans in the upper
left are the +15 and -15 volt supplies for the analog Op amps,
sample/hold and DAC circuits comprsing the left analog part fo the
The uP is an 1802.
DAC1006 D/A converters are used both for A/D conversion with a
comparator and for D/A output to the meter and Ultra-Stable Oscillator.
A1A4 12.6 MHz Synthesizer
another same size board, the A1A4 12.6 MHz
Synthesizer (56219 Assy) that shares the same 14 conductor ribbon cable
and has a single coax cable that goes to the times 18
Multiplier. There are a half dozen Synchronous Four-Bit
ICs on this board.
A1A1 Cesium Beam Tube Assembly (Physics Package)
the photo gives it a curved appearance
because of perspective.
A1 Cesium beam tube is held at each
end by an angle bracket that has 3 large philips screws holding it to
the 5030 frame. One of these is under the A8 power supply and the
other is under the A3 uP board.
The x51 Multiplier and the Cesium Beam Tube Interface PCB are attached
to the tube.
Connections to the rest of the system are by means of:
Red & white High voltage wires, twisted pair of orange wires to Cs
coax with 180 MHz from A7 to X51 mult.
26 conductor ribbon cable to mother board W5
Coax with error signal from interface board to A3 uP board.
the wires coming out of the CBT are
soldered. The E26 Test Point is missing. The wires coming
from theDetector Heater are labeled along with the "E" number of the
X51 Microwave Multiplier
The x51 Microwave multiplier gets it's RF input from the A1A7 X18
Multiplier - Mixer and feeds it's output to the waveguide adapter on
the CBT. The Red, Green and Black wires come from the CBT
PCB Rails but no Card Edge Connectors
The PCBs are held by rails, but there are no card edge connectors on
the PCBs. All connections are made by coldered wires, coax
connectors (typcially standard 50 Ohm SMB), or rectangular
connectors. There is an unused pair of rails above the
microprocessor PCB, but if another board is used there it would ned to
have notches to clear the to coax connectors coming from the uP board.
Manual Control Voltage & Loop Gain Setting
In Appendix A of the Operation Manual
it describes how to manually set the Control Voltage and Loop
Gain. The symptom indicating that this needs to be done is that
when the Monitor is set to 4, Control Voltage, the needle ramps up and
jumps down and this is repeated over and over. This was the
symptom my unit had so I manually adjusted these two settings as
follows after over 30 minutes of warm up:
- Open door and turn off "MOD" and set "LOOP" to OPEN, then
- At the same time press "Align" (behind the door) and "Operation
Alarm" (next to the Monitor LED). This stops the control voltage
- Set the "Manual Scan" switch (behind the door) to "Control
Voltage" and set the Monitor switch to 4 (control Voltage) and use the
"Manual Scan Increase/Decrease" switch to center the meter.
- Set the "Manual Scan" switch (behind the door) to to "Loop Gain"
and set the Monitor switch to 3 (Beam) and and use the "Manual Scan
Increase/Decrease" switch to center the meter.
- Switch the "MOD" and "LOOP" switches back to On and Closed.
In my case this caused the Lock LED to turn on and stay on.
26 Feb 2006 - Note after almost getting
the C field set on s/n 1013, there was a power failure lasting about 2
seconds. But 1013 had been running for many months and was
working well. After the power came back on the lock LED did not
light. After giving it about 4 hours still with no lock light,
the above procedure was used to set the control voltage and loop gain,
and afterwards the lock LED turned on as soon as the closed loop and
mod on switches were thrown.
28 Apr 2006 - You really can only center the Control Voltage using the
front panel controls (as described above in the OPEN mode). When
there's a continuous search or the yellow monitor LED is on with the
green LOCK LED, then it's time to adjust the coarse frequency of the
crystal oscillator. This can be done with the source
locked. Remove the bottom cover and with the monitor switch in
position 4 (CONTROL) note the reading. In my case it was over
3. Then adjust the coarse pot on the USO to bring the needle a
little to the other side of 2.5, in my case to 1.6. When the
control voltage gets closer to 2.5 the yellow monitor LED will go out
leaving only the two green LED for LOCK and AC power.
Hint: leave the door slightly open by turning the screw all the way
out, closing the door and then turning the screw 1/4 turn. This
way if the ALIGN lamp turns on you can see it. You could leave
the door open, but for me it's in the way of other stuff.
Manual Loop Gain
PCB there are 2 10-turn pots. The one
close the the SMB connector is R9 and should not be changed. The
one next to R9 is R5 and is the manual beam current adjust. It
should be set so that the voltage between E23 (ground) and E26 (a test
point) is 1.8 +/- 0.2 VDC. But I can't find E26 on my unit.
Where is it?
Also note in the photo there is a small screwdriver adjustment on top
of the 10 MHz OCXO that has been relocated from the front so that you
do NOT need to remove the 5030 Assembly to get access to this coarse
Serial Number 1013 has had the Green Lock LED on for about 3
hours. If the line cord is removed and plugged back in after 15
seconds the unit Lock LED turnes on in about 10 minutes.
The manual implies that you can make
the loop gain or beam current adjustments on the fly. But on the
two occasions that I have tried to do that the FTS4060/S24 gets
confused. The fix has been to pull the line plug for about 15
seconds and restart. Without the restart the control loop is
makes a good accessory. It
provides a UTC clock, 1 PPS output and a check on the stability of the
FTS4060. Also if the reference input fails the 2100T will break
lock and need to be manually re started and so it's a good monitor on
the output of the reference source.
If you have one of the /S24 units would
you tell me if you have the 10 MHz output and your serial number?
If you have brought a unit back to life tell me what you did. email to